A 7a-methoxycephalosporin derivative and process for producing the same

A 7 alpha -methoxycephalosporin derivative represented by the formula (I): <IMAGE> wherein R1 represents a heterocyclic ring or an -S- heterocyclic ring; R2 represents a hydrogen atom, a carboxy group or a -COOR5 group wherein R5 represents a C1-6 alkyl group, a dialkylamino-C1-6 alkyl group or a <IMAGE> group wherein R6 represents a C1-6 alkyl group, a C1-6 acyl group or a (C1-6 alkoxy) carbonyl group and Y represents a hydrogen atom or a C1-6 alkyl group; R3 represents a hydrogen atom, a carbamoyl group or a C1-6 acyl group; R4 represents a hydrogen atom, a C1-6 alkyl group, a dialkylamino-C1-6 alkyl group or a <IMAGE> group wherein R6 and Y are defined as above; A and B, which may be the same or different, each represents a straight chain or branched chain alkylene group having 1 to 5 carbon atoms; and x represents 0 or 1; or a pharmaceutically acceptable salt thereof.